US3895382A - Method and apparatus for measuring passively range and bearing - Google Patents

Method and apparatus for measuring passively range and bearing Download PDF

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US3895382A
US3895382A US438297A US43829774A US3895382A US 3895382 A US3895382 A US 3895382A US 438297 A US438297 A US 438297A US 43829774 A US43829774 A US 43829774A US 3895382 A US3895382 A US 3895382A
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signals
transponder
aircraft
bearing angle
representative
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George B Litchford
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Litchstreet Co
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Litchstreet Co
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S11/00—Systems for determining distance or velocity not using reflection or reradiation
    • G01S11/02—Systems for determining distance or velocity not using reflection or reradiation using radio waves
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
    • G01S13/88—Radar or analogous systems specially adapted for specific applications
    • G01S13/93—Radar or analogous systems specially adapted for specific applications for anti-collision purposes
    • G01S13/933—Radar or analogous systems specially adapted for specific applications for anti-collision purposes of aircraft or spacecraft
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
    • G01S13/74—Systems using reradiation of radio waves, e.g. secondary radar systems; Analogous systems
    • G01S13/76—Systems using reradiation of radio waves, e.g. secondary radar systems; Analogous systems wherein pulse-type signals are transmitted
    • G01S13/78—Systems using reradiation of radio waves, e.g. secondary radar systems; Analogous systems wherein pulse-type signals are transmitted discriminating between different kinds of targets, e.g. IFF-radar, i.e. identification of friend or foe
    • G01S13/781—Secondary Surveillance Radar [SSR] in general

Definitions

  • the slant range to the 52 3 g transponder equipped aircraft is then computed in ac- 'g g'l3 211971 2:11; 343,6 5 R cordance with a predetermined relationship between 3:626:41] l2/l97l Lirchr ra iljun ij..,...I: 343/63 x helime of of one of "ansponder replies Reese and the bearing angle.
  • the present invention pertains to radiolocation of mobile vehicles within the coverage of at least two scanning radars of a standard secondary radar system.
  • the invention concerns a collision avoidance/proximity warning system, capable of determining the slant range and relative bearing to a nearby mobile vehicle, that is based on signals emitted by secondary radars, such as the National Air Traffic Control Radar Beacon System (ATCRBS) and the International Civil Aviation Organization (ICAO) Secondary Surveillance Radar System.
  • secondary radars such as the National Air Traffic Control Radar Beacon System (ATCRBS) and the International Civil Aviation Organization (ICAO) Secondary Surveillance Radar System.
  • SSR secondary surveillance radar
  • transponders carried on aircraft to discriminate against interference and ground clutter and to provide for automatic transmission of identification and other data, such as altitude, from the aircraft to the ground-based radar.
  • a traffic controller observing the radar display directs the pilots of the involved aircraft by radio, usually with voice communication, so as to maintain or restore safe separations between aircraft.
  • Such a system of traffic control and separation assurance is limited in capability because each aircraft must be dealt with individually and requires its share of the controller's time and attention and its share of the available radio spectrum. When traffic is heavy, takeoffs and landings are delayed, and the possibility of col lision increases.
  • Collision avoidance system means an all weather cooperative system on an aircraft which is compatible with but independent of ground-based air traffic control systems and can detect all other aircraft representing a potential collision threat and, if necessary, indicate to the pilot a safe evasion maneuver.
  • COLLISION AVOIDANCE SYSTEMS d. (I). Minimum standards pursuant to this section shall include the requirend that within a reasonable time after its enactment (A) a collision avoidance system shall be installed on any aircraft which is operated by an air carrier or a supplemental air carrier, and has a maximum certificated takeoff weight in excess of sixty thousand pounds;
  • bearing angle is meant to define the angle from the collision avoidance system equipped aircraft (own aircraft) and azimuth angle is.meant to define the angle from the ground SSR, to either the own aircraft or the other aircraft.
  • a collision avoidance system installed in an own aircraft which includes line of position circuitry for determining the azimuthal lines of position to the own aircraft and to another aircraft from interrogating ground stations and which includes time of arrival circuitry for determining the times of arrival at the own aircraft of the transponder replies by the other aircraft to the interrogating signals emitted by the ground stations and received by both aircraft.
  • the system calculates the bearing angles to the actual and imaginary locations of the other aircraft
  • the signals representative of the bearing angles to such actual and imaginary locations of the other aircraft are supplied to truth table circuitry wherein a decision is made as to which signal represents the bearing angle to the actual location of the other aircraft and wherein the signal representative of the bearing angle to the imaginary location is eliminated.
  • the slant range is then computed from a predetermined relationship between the time of arrival of a reply from a selected one of the ground stations and the associated bearing angle.
  • Ax is the angular difference between the two azimuthal lines of position to the aircraft
  • T, and T are the times of arrival of the replies from the other aircraft to the interrogating signals of the two ground stations.
  • the bearing angles to at least four possible locations of such other aircraft are computed in accordance with the foregoing equations.
  • the parameters At, T, and T will vary in accordance with the identity of the ground stations interrogating the aircraft.
  • the timing sequences of the associated interrogation and reply signals are compared in lead/lag circuitry to develop signals. against which the signs of the calculated bearing angle signals are compared in the truth table to determine which of the computed bearing angles represents the bearing angle to the actual location of the other aircraft.
  • the truth table comprises circuitry for comparing the multiple bearing angles as measured from a selected azimuthal line of position to determine coincidence thcrebetween. Such coincidence permits the selection of the bearing angle to the actual location of the other aircraft Once the bearing angle is known.
  • the slant range to the other aircraft is calculated according to the following equation:
  • a is one-half the sum of the azimuth angles (ar 01,) from the first SSR ground station to the own aircraft and the other aircraft
  • B is one-half the sum of the azimuth angles (B 13,) from the second SSR ground station to the own aircraft and the other aircraft
  • FIGS. 1A, 1B, 1C and 1D are geometrical diagrams useful in understanding the derivation of bearing angles in accordance with the present invention.
  • FIG. 2 is a geometrical diagram useful in explaining the preferred embodiment of a collision avoidance system shown in FIG. 3;
  • FIG. 4 is a geometrical diagram useful in explaining the preferred embodiment of a collision avoidance system shown in FIG. 5;
  • an SSR ground station In the standard ICAO secondary surveillance radar system, an SSR ground station repeatedly transmits interrogations at a frequency of 1030 MHz on a continuously rotating beam.
  • the beam which is conventionally controlled by the strength of side lobe suppression signals to a width of 4, scans the surrounding area in the clockwise direction, completing one revolution in a period of approximately 4 to ID seconds.
  • the SSR ground stations In the United States, the SSR ground stations are installed in a random pattern across the country, the density of which generally varies in accordance with the density of air traffic.
  • All commercial transport aircraft and nearly all other aircraft that utilize major airports are equipped with transponders which reply to interrogations received from SSR ground stations.
  • SSR beam scans past an aircraft, it interrogates that aircraft transponder from about to 25 times at precise intervals which are indigenous to each station, e.g., 2 to 5 msec.
  • Each interrogation initiates a reply transmission from the transponder at a frequency of 1090 MHz.
  • the transponder reply message includes two socalled framing pulses" which are spaced apart in time by 20.3 microseconds.
  • the interval between the framing pulses contains a number of discrete sub-intervals, in each of which a pulse may or may not be transmitted, depending upon what information is to be contained in the reply. Twelve such sub-intervals are available, permitting 4,096 different binary code groups, each representing one or more pieces of information such as identity, barometric altitude, distress signal, and so on.
  • the desired reply code group now internationally standardized, may be set into the transponder by the operator of the aircraft using manual code wheel switches, or in some cases automatically by an altimeter or even semiautommatically, for example by pressing a button.
  • each aircraft transponder is interrogated by each ground station to alternately transmit the identity (A mode) and the altitude (C mode) of its aircraft.
  • the replies to these alternate interrogations can be decoded at the SSR ground station and utilized to place both identity and altitude on the radar display of the ground controller adjacent the spot which represents the aircraft that is transmitting the replies.
  • a common radio channel allows the airborne transponder to reply to all ground interrogators within line of sight.
  • the first framing pulse (F, of the reply of a transponder follows the end of a received interrogation by a standard delay of 3 usec.
  • the second framing pulse (F is transmitted 20.3 usee after the first framing pulse.
  • the transponder is then automatically disabled for an interval of about 45 to I25 psec. called the dead time.
  • the system of the present invention is fully compatible with the present United States and [CAD secondary surveillance radar system and utilizes the I030 MHz interrogations and the 1090 MHz replies thereto to determine passively the bearing angle and slant range between closely spaced aircraft.
  • the present system meets the requirements of the foregoing proposed legislation which would mandate that a collision avoidance system be installed on all air carriers, all public aircraft and large civil aircraft, and that such systems be designed to respond to signals automatically generated by the transponder in any small civil aircraft not required by the legislation to have a collision avoidance system.
  • FIGS. 1A, 1B 1C A discussion first of FIGS. 1A, 1B 1C and the mathematical basis for passive range measurements is useful to an understanding of the present invention.
  • the own station is shown at the origin, while a single wavefront is shown travelling in the y direction from a very distant radar.
  • the front reaches simultaneously the own station and another possible station T, units to the right of the own station.
  • a signal is initiated from the other station and travels to the own station, arriving at a time A! later.
  • the difference between the time of arrival (TOA) of the wavefront and the time of arrival of other stations signal corresponds to the distance T,.
  • TOA time of arrival
  • FIG. 1A illustrates the case when the radar wavefront arrives at the own station first.
  • the point(O. T l2l on the y axis typically satisfies this condition.
  • FIG. 18 illustrates the case when the wavefront arrives at the unknown other station first. In this case,
  • FIG. 1C illustrates two wavefronts, one originating from a distant radar with an azimuthal angle of 0 and with a TOA difference T and the other wavefront originating from second radar with an angle of (1 and a TOA difference T
  • the two parabolas intersect at only two precise points which may be determined as follows:
  • the unknown station's deviation may be specified:
  • the bearing angle to the real location of the unknown station is determined as follows: First, the two 0 values are computed in accordance with equation (1). Then. for radar l, a determination is made as whether the unknown station is leading or lagging. For the proper deviation, a selection as to which of the computed bearing angles satisfy the limits of condition. If only one 0 satisfies condition I, the correct 0 has been found. Condition 2 is not then required. If both 0's meet condition I, the process is repeated for condition 2. Only the correct 9 will satisfy condition 2. With the proper 6 determined. substitution in the basic 65 parabola l R l cos will give the range,
  • FIG. ID illustrates the general case with radars emitting from azimuths a, and 0: as shown with TOA differences T, and T respectively.
  • FIG. 2 illustrates the geometrical relationships between the signals in an airspace occupied by a reference or own aircraft incorporating a collision avoidance system, referred to as an A type aircraft and an unknown aircraft a plane within a preselected proximity to the A aircraft and without such a system, referred to as a D type aircraft.
  • the interrogations are received at different angles and different times by the A aircraft and the D aircraft equipped only with a conventional SSR transponder.
  • the air-to-air separation between the aircraft is significantly smaller than the distance between the aircraft and the interrogating ground stations so that the angles at which the A and D aircraft receive interrogations are virtually the same.
  • the lines of position (LOPs) to the two aircraft from each ground station can be considered parallel.
  • a is the azimuth angle at which the A and D aircraft receive the 1030 MHz interrogations from SSR-l as measured from the magnetic north of such ground station.
  • the magnetic north reference is available in the aircraft and is independent of the heading of the aircraft.
  • a is 0 in FIG. 2.
  • a is the azi muth angle at which the A and D aircraft receive the 1030 MHz interrogations from the ground station SSR-2 as measured from its magnetic north.
  • a is 90 in FIG. 2, 0: equals 01 a, or 90.
  • parabolic contours T and T are shown as representative of the two times of arrival for the reply signals generated by the D aircraft.
  • the assumption ofa parabolic curve surrounding one of the foci of an ellipse (A aircraft) is acceptable as long as the major axis of the ellipse is several times greater than the minor axis.
  • such assumption need not be made and the actual elliptcal contours for the times of arrival T and T may be used.
  • the differences between the azimuthal lines of position to the A and D aircraft may be computed and thus used in computing bearing angles.
  • the mathematical expression is rendered more complex. The assumptions here then as to time of arrival contours and azimuthal lines of position are made principally to simplify the explanation of the present invention.
  • the curves T and T intersect at two points, one representing a true crossing (a real D aircraft location) and the other representing a false crossing (an imaginary D aircraft location).
  • Such understanding is necessary in as much as the transponder replies of the D aircraft to the interrogations by SSR-l and SSR-2, as detected by the A aircraft, will permit the developement of two time of arrival (TOA) values which will locate the D aircraft in two locations, the real and imaginary.
  • TOA time of arrival
  • 0A is the bearing angle measured at the A aircraft from LOP-l to the false crossing
  • 08 is the hearing angle measured at the A aircraft from LOP-l to the true crossing
  • 0A and 68 are the bearing angles measured from the A aircraft relative to LOP-2 to the false and true crossings, respectively.
  • the collision avoidance system of the present invention installed in ones own aircraft (an A, B or C type aircraft using the legislative denominations) includes a first receiver 20 tuned to receive RF transmission signals at I030 MHz and a second receiver 22 tuned to receive signals at I090 MHz.
  • the 1030 MHZ receiver 20 is adapted to receive the SSR-l and SSR-2 interrogations which trigger a transmitter to emit I090 MHz reply messages in response thereto.
  • the I090 MHz receiver receives and decodes the transponder replies of the D aircraft, including the D aircraft's identity and altitude. Since it is not a part of the present invention, there is not shown in FIG. 3 (or FIG. 5) apparatus for monitoring an azimuth sector wider than the rotating main beam of the radar. Such apparatus (which will be utilized) is shown in the Litchford U.S. Pat. No. 3,735,408 and the disclosure of this patent is incorporated herein by reference.
  • the system comprises a pair of pulse repetition frequency (PRF) selectors 24A and 248 which simultaneously tune" the system to the unique pulse repetition frequencies of SSR-l and SSR-2 ground stations and no other.
  • PRF pulse repetition frequency
  • SSRs may be simply modified to transmit omnidrectionally three pulses, the normal P the normal P and P A, and P 8 spaced two microseconds apart each time the scanning beam rotates through magnetic north. This triad of pulses could be encoded into a single omnidirectional burst of north pulses by any number of known ways.
  • the A circuitry produces signals representing the line of position to the fixed ground station SSR-l as measured from its magnetic north (01,) in the following manner: whenever the L030 MHZ receiver receives a burst of several north pulse triads, the burst envelope is detected by the decoder 26A and a signal is applied to the timers 30A and 32A to turn them on.
  • the beam interrogations are detected by the decoder 28A and a signal is applied to the timer 30A to cause the transfer of an accumulated time value to its output buffer.
  • the time value accumulated by the timer 32A is transferred to its output buffer upon receipt of the next north pulse burst, i.e., every complete rotation by the beam.
  • the respective buffers supply these time values to the ratio circuit 34A which retains such values until new time values are computed and the buffers updated.
  • SSRs rotate at different angular velocities requiring circuitry to accommodate any rotational period by the scanning beam.
  • the ratio circuit 34A determines the ratio between the signal received from the timer 30A and the signal received from the timer 32A to produce an output signal of proper scale, representing the angle a, in degrees.
  • the angle a will be computed as (360/8) or 45".
  • the circuits 26B 34B operate in the same manner to determine the line of position (01 to the SSR-2 as measured from magnetic north.
  • the signals representing the angles a, and or, are passed along correspondingly labelled conductors to a combining circuit 36 where the values of the two signals are subtracted from each other.
  • the output signal, denoted 01 represents the angular difference clockwise between LOP-l and LOP-2 using LOP-l as the reference.
  • the collision avoidance system of the present invention comprises a pair of PRF selectors 40A and 408 which, like the selectors 24A and 24B, respond only to the interrogations of the SSR-l and SSR-2 ground stations.
  • the interrogation signals are passed on to the input terminals of a pair of gates 42A and 428 which are enabled by the P pulses of the L030 MHZ interrogations.
  • the P pulses are supplied to a pair of interval timers 44A and 448 to clear the timers and turn them on.
  • the transponder reply signals of the D aircraft detected by the L090 MHz receiver 22 are supplied to a pair of reply, altitude and identity decoders 46A and 468 which decode the replies and supply them to the other input terminals of the gates 42A and 423.
  • the reply decoders respond to the mode C replies that indicate the intruder aircraft is within a predetermined common altitude band.
  • the decoders decode the altitude mode C replies to ascertain the altitude of the other aircraft and also produce signals representative of its own aircrafr. The signals are compared to produce common altitude stratum signals if the altitudes are with a selected range, e.g., $2000 feet.
  • the decoders 46A and 46B decode the mode A signals to identify the other aircraft.
  • the decoders 46A and 468 may be tied together through a comparator in order to assure correspondence between the identity of the reporting other aircraft. In this way, replies from aircraft beyond a certain common altitude stratum or from different aircraft will be discarded.
  • the gates enabled by the P pulses of the associ atcd interrogations supply the replies to the interval timers 44A and 448 to turn the timers off.
  • the output signals developed by the timers 44A and 44B represent the times of arrival of the reply signals at the own or A aircraft generated by the transponder of the D aircraft in response to interrogations by the SSR-l and SSR-2 ground stations.
  • the conversion of TOA values representing the parabolas may be made by dividing the time values by 6.1838 microseconds since radiation travels I NM in 6.l838 microseconds. With such conversion, the time of arrival values in terms of geographic parabolas, designated herein as T, and T (corresponding to SSR-l and SSR-2, respectively), are determined. The T, and T signals are carried along correspondingly labelled conductors.
  • the system further includes a pair of lead/lag circuits 47A and 47B which develop either negative or positive voltage levels in response to the timing sequence of the 1030 MHz interrogation signals and the reception of the 1090 MHz reply signals.
  • the reply signals as detected by the L090 MHz receiver 22 are also supplied to the input terminals of the circuits 47A and 47B and the interrogation signals, as detected by the selectors 40A and 40B are supplied to other input terminals of the circuits 47A and 47B.
  • the plus or minus signals developed by the lead/lag circuits form part of a truth table, explained hereinafter, which resolve the ambiguities resulting from the dual crossings of the wavefronts T, and T
  • the plus or minus voltage level signals developed by the circuits 47A and 47B are carried by conductors 48A and 488, respectively. It is noteworthy that in addition to the lead/lag data, the azimuthal separation between the A and D aircraft relative to selected SSR stations may be determined. This angular difference (assumed to be zero in the FIG. 2 diagram) and its polarity is utilized in mathematical solution for determining bearing angle and range given hereinabove.
  • the signals representative of the times of arrival T, and T and the signal (a) representative of the angular difference between the lines of position are supplied to a logic circuit 49 wherein the bearing angles 6A, and 6B, are computed in accordance with the following formulae:
  • the signals representative of the computed bearing angles 0A, and 0B are carried along correspondingly designated conductors to combining circuits 50A and 50B and to a pair of sign detector circuits 52A and 528.
  • the signal representative of the angular difference between LOP-l and LOP-2 is subtracted from the 6A, and 6B, signals to develop signals representative of bearing angles 0A and 6B
  • the 0A and 0B, signals are likewise supplied along correspondingly labelled conductors to a pair of sign detector circuits 54A and 54B.
  • the signals are compared against a fixed reference signal representing 180 to develop positive signals in the event the supplied angles are less than 180 and negative signals in the event the supplied angles are greater than 180.
  • the four outputs from the sign detector circuits 52A, 54A, and 52B, 548 will become combination of positive and negative voltages which contain the required information to permit the selection of the bearing angle to the actual location of the D aircraft.
  • the imaginary location or ambiguous second crossing of the two parabolas is identified as false and eliminated.
  • the circuitry for eliminating the false crossing and determining the true bearing angle comprises a comparator circuit 56A to which the sign of the 0A, signal is supplied, a comparator circuit 58A to which the sign of the 6A, signal is supplied, a comparator circuit 56B to which the sign of the 0B, signal is supplied and a comparator circuit 588 to which the sign of the BB, signal is supplied.
  • the other input terminals of the comparators 56A and 56B are supplied with either positive or negativie voltage levels from the lead/lag circuit 47A.
  • the comparator circuits 58A and 58B are supplied with positive or negative voltage levels developed by the lead/lag circuit 478.
  • the lead/lag circuits 47A and 47B develop positive voltage levels in response to the early detection of the 1,030 MHz interrogation of the A aircraft and negative voltage levels in response to the early detection of the L090 MHz replies from the D aircraft.
  • the comparators are designed to operate in response to preselected polarities appearing at their input terminals.
  • the comparators 56A and 58A respond only to either two positive or two negative input signals to supply positive output signals along a conductor leading to an AND gate 60A, referred to as the BA, truth gate.
  • Comparators 56B and 58B are likewise designed to respond to either two positive or two negative input signals to supply positive output signals along conductors leading to an AND gate 608, designated as the 0B, truth gate.
  • the comparators supply negative output signals.
  • the gates 60A and 60B which may be of typical AND" gate construction respond to positive input signals of equal amplitude to supply enabling signals along conductors leading to a pair of transmission gates 62A and 628.
  • the other input terminals of the transmission gates 62A and 62B are supplied with the signals representative of the bearing angles 0A, and 6B,, respectively.
  • the transmission gate 62A or 628 will transmit the true bearing angle, be it 6A, or 98, to a logic circuit 64 wherein the range between the A and D aircraft is calculated.
  • the circuit 64 calculates the range (R) in accordance with the following equation:
  • 6A, and B are the bearing angles as measured at aircraft A relative to the line of position from SSR-l to the D aircraft.
  • the output terminals of the transmission gates 62A and 62B are also supplied to a logic circuit 70 where the signals representative of such bearing angles are combined with the signal representative of the angle a, to develop a signal representative of the true bearing angle. This angle is then displayed by a bearing angle indicator 72.
  • range and range rate can be combined to obtain the value TAU, or time to collision. if the TAU value is small enough, a command signal is generated which directs the pilot to climb or descend to avoid the approaching aircraft. Bearing angle, range rate and range may be combined to restrict the generation of command signals to those instances where there is a real possibility of a collision. Specifically, the transverse velocity of the other aircraft may be calculated from such signals. If the velocity is increasing, the TAU circuitry will be inhibited. If the velocity is decreasing, the TAU circuitry will be enabled and the pilot directed to take corrective action immediately. The TAU logic is described in detail in the Air Transport Association's report entitled ANTC-l 17''.
  • comparators 56A and 58A will be disabled; comparators 56B and 583 will be enabled.
  • the B truth gate 608 will likewise be enabled and the value of 6B,, the true bearing angle transmitted to logic circuit 64. False bearing angle 0A, is eliminated.
  • the range R may then be calculated as follows:
  • R l+cos222
  • the collision avoidance system of FIG. 3 utilizes the interrogation of a pair of SSR ground stations and the D aircrafts replies thereto to compute the range and bearing angle from the A aircraft to the D aircraft. When more than two ground stations are available, the computation is technologically simplified.
  • FIG. 4 there are shown three fixed ground stations labelled SSR-l, SSR-2 and SSR-3, respectively, which interrogate an A aircraft and a D aircraft located in a selected proximity to the A aircraft.
  • the A aircraft is shown as a triangle, while the D aircraft is shown as a circle.
  • the lines of position to the A aircraft are labelled LOP-l, LOP-2 and LOP-3.
  • Parabolic contours for the TOA signals as measured by the A aircraft are labelled T,, T and T respectively.
  • the contours have approximately parabolic shapes (actually elliptical), with each of the parabolas intersecting at two points, a true location and a false location of the intruder or D aircraft.
  • intersections of the parabolic wavefronts T T and T at the true location of the D aircraft are labelled A, C and E; A representing the crossing T T C representing the crossing T,-T and E representing the crossing T T.
  • a representing the crossing T T C representing the crossing T,-T and E representing the crossing T T The false crossing of the two parabolas T, and T is indicated by the letter B, the false crossing of the parabolas T, and T is indicated by the letter D and the false crossing of the parabolas T and T is indicated by the letter F.
  • the collision avoidance apparatus shown in FIG. utilizes the lines of position to the ground station SSRs and the times of arrival of the three transponder replies to these same SSRs of the interrogated D aircraft to calculate the bearing angle and slant range to such D aircraft.
  • the system includes a L030 MHZ receiver and a 1,090 MHz receiver 82.
  • line of position (LOP) circuits 84A, 84B and 84C are also provided, exemplary configurations of which are shown in FIG. 2 and described hcreinabove, which calculate the azimuthal lines of position 11,, a and a from the A aircraft to SSR-l, SSR-2 and SSR-3 ground stations. respectively.
  • time of arrival calculation circuits 86A, 86B and 86C are identified by the letters T T and T respectively.
  • the conductors to which the signals are supplied are identified by the same letters.
  • the a and a signals are supplied to a combining circuit 88 wherein the a signal is subtracted from the 0: signal to provide an angular difference signal ax. Similarly, the a, signal is subtracted from the (1 signal in a combining circuit 90 to provide as an output the angular difference signal cry.
  • the angular difference signal 00: and the signals representative of the times of arrival T and T are supplied to logic circuit 92 wherein the angles 6A and 6B, are computed in accordance with the following formulae:
  • the signals representative of the computed angles BA BB BC, and 0D, are then supplied along correspondingly labelled conductors to four combining circuits 96, 97, 98 and 99 where the angles representative of true and false crossing points are subtracted.
  • Signals with magnitudes representative of the angular differences as determined by the circuits 96, 97 and 98, 99 are then supplied to a pair of selector circuits 100 and 102. respectively. which transmit only the signals with the smallest magnitudes.
  • the selector 100 supplies a zero voltage signal output.
  • the selector 102 supplies a signal output having a magnitude representative of the smallest angular variation between the angles 6B,. 0C. and 05,. 0D,.
  • the smallest angular variation signals are then supplied to a comparator 104 which compares the two signals and. depending on which of the signals has the smallest magnitude supplies an enabling signal to A enable gate 106 or an enabling signal to a 9B, enable gate 108.
  • Logic circuits 92 and 94 supply the (9A and 6B, signals to the other input terminals of the gates I06 and 108, as indicated by the conductors labelled 8A. and 63 Thus. depending upon which of the gates I06 and 108 is enabled, the gate will transmit the true bearing angle. either 6A, or 08.
  • a logic circuit 110 wherein the range between the A and D aircraft is determined. According to the present invention, the circuit 110 calculates the range in accordance with the equation:
  • R l cos 9 where 0 will be either 0A, or 68.
  • the signal T is supplied along the conductor labelled T to another input terminal of the circuit 110 in order to implement the calculation.
  • the range representative signal is supplied concurrently to a range indicator 112 and a range rate indicator 114.
  • the range indicataor displays the range. while the range rate indicator 114 displays the range rate in knots.
  • 49A and 0B are the bearing angles as measured from the line of position of the A aircraft to the SSR-l ground station.
  • a circuit 116 is thus provided which combines the angle a, which is the angle between magnetic north and LOP-1 with either 0A. or 0B. depending upon which of the gates 106 or 108 is enabled.
  • the resultant signal represents the true bearing with respect to magnetic north.
  • the system of FIG. utilizes two or more coincident bearing angles measured from a selected line of position. whereas the system of FIG. 3 utilizes lead/lag logic to separate the true crossing from the false crossing.
  • lead/lag logic to separate the true crossing from the false crossing.
  • the elliptical contour of the curve surrounding one of the foci of an ellipse (own aircraft) is utilized. with bearing angle and slant range being computed in accordance with the equations given hereinabove. Also. the own aircraft may estimate the range to the SSR ground stations. as well as to the other aircraft.
  • a system for collision avoidance and/or proximity warning indication at an own location utilizing the signals transmitted by scanning beam secondary surveillance radar (SSR) stations and reply messages transmitted by a nearby transponder replying to said SSR signals.
  • apparatus for passively determining the bearing angle from said own location to said transponder comprising:
  • c. means responsive to signals representative of selected azimuthal lines of position and to the corresponding signals representative of selected times of arrival for providing a signal indicative of the bearing angle from the own location measured from said lines of position to the location in space from which the transponder replies originate.
  • Apparatus according to claim 1 for passively determining the range to said transponder from said own location comprising:
  • d. means responsive to one of said selected times of arrival representative signals and the signal indicative of the bearing angle for providing a signal representing the distance separating said transponder from said own location.
  • Apparatus according to claim 3 further comprising:
  • Apparatus according to claim 2 further comprising:
  • first indicator means responsive to said range representative signal for displaying the distance separating the own location from said transponder
  • second indicator means responsive to said range representative signal for providing signals indicative of the rate of change of said range representative signal and constituing means for displaying said range rate.
  • Apparatus according to claim 2 comprising:
  • third indicator means responsive to the bearing angle representative signal for displaying the bearing of said transponder.
  • the means for providing a bearing angle indicative signal comprises means responsive to the signals representative of selected azimuthal lines of position and to the corresponding signals representative of selected times of arrival for providing signals indicative of the bearing angles from the own location measured from said lines of position to the locations in space from which transponder replies actually originate and from which transponder replies apparently originate.
  • the means for providing a bearing angle indicative signal comprises means responsive to signals representative of selected azimuthal lines of position originating from geographically separated SSR stations for providing signals representative of the angular differences between said selected azimuthal lines of position and means responsive to said angular difference signals and to signals representative of the corresponding times of arrival for generating said actual and apparent bearing angle indicative signals.
  • Apparatus according to claim 7 further comprising:
  • truth table means responsive to preselected relationships between said bearing angle indicative signals, said truth table means comprising means for identifying said signals as indicative of either the true bearing angle to the locations in space from which the transponder replies actually originate or the false bearing angles to the locations in space from which the transponder replies apparently originate and means for transmitting the signal representative of the actual bearing angle and blocking the signals representative of the apparent bearing angles.
  • Apparatus according to claim 9 wherein two secondary surveillance radar stations interrogate said own location and said transponder and wherein the truth table means comprises means for assigning said actual and apparent bearing angle representative signals selected polarities in accordance with their angular magnitudcs, lead/lag logic means responsive to the reply messages transmitted by said transponder for developing signals with selected polarities in accordance with the azimuthal positioning of said transponder relative to the own location's azimuth from the secondary surveillance radars, means for comparing said assigned polarities and the signals developed by said lead/lag logic means to determine the true bearing by polarity, and means controlled by said comparator means for transmitting the actual bearing angle representative signal and eliminating the apparent bearing angle representative signals.
  • Apparatus according to claim 9 wherein at least three secondary surveillance radar stations interrogate said own location and said transponder and wherein said means for providing a bearing angle indicative signal comprises means responsive to selected azimuthal lines of position and to corresponding signals representative of selected times of arrival for developing signals indicative of at least four bearing angles as measured from the azimuthal lines of position from one of said secondary surveillance radar stations to the locations in space from which transponder replies actually and apparently originate.
  • the truth table means comprises compartor means responsive to said bearing angle indicative signals for determining the coincidence in magnitude between two of said bearing signals, such two signals being essentially equal and consequently representative of the actual bearing angle, and further comprising means controlled by said comparator means for transmitting the actual bearing angle representative signal and eliminating the apparent bearing angle representative signals.
  • a method for passively determining the bearing of a transponder within a selectable proximity to ones own position from the interrogation replies of the transponder in the coverage of a secondary radar system comprising the steps of:

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US4115771A (en) * 1976-05-11 1978-09-19 Litchstreet Co. Passive ATCRBS using signals of remote SSR
US4293857A (en) * 1979-08-10 1981-10-06 Baldwin Edwin L Collision avoidance warning system
US4486755A (en) * 1982-02-22 1984-12-04 Litchstreet Co. Collision avoidance system
WO1985004259A1 (en) * 1984-03-14 1985-09-26 Litchstreet Co. Simple passive/active proximity warning system
DE3637129A1 (de) * 1986-10-31 1988-05-11 Deutsche Forsch Luft Raumfahrt Verfahren zur positionsbestimmung eines flugzeuges in einem dreiweg-dme-system
US4768036A (en) * 1985-10-16 1988-08-30 Litchstreet Co. Collision avoidance system
US4789865A (en) * 1987-10-21 1988-12-06 Litchstreet Co. Collision avoidance system
US4894810A (en) * 1986-01-28 1990-01-16 Mikrovalmiste U.J. Pulkkanen Oy Method and a device for measuring a distance by means of ultrasonic pulses
US4910526A (en) * 1987-05-18 1990-03-20 Avion Systems, Inc. Airborne surveillance method and system
US5075694A (en) * 1987-05-18 1991-12-24 Avion Systems, Inc. Airborne surveillance method and system
US5327145A (en) * 1990-05-22 1994-07-05 Hughes Aircraft Company Time delay passive ranging technique
US5552788A (en) * 1995-06-30 1996-09-03 Ryan International Corporation Antenna arrangement and aircraft collision avoidance system
US20030142002A1 (en) * 2000-05-09 2003-07-31 Karl Winner Vehicle surveillance system
US20050024256A1 (en) * 2003-07-29 2005-02-03 Navaero Ab Passive Airborne Collision Warning Device and Method
US20050073439A1 (en) * 2003-10-01 2005-04-07 Perricone Nicholas V. Threat detection system interface
US20090231181A1 (en) * 2008-01-31 2009-09-17 Bae Systems Information And Electronic Systems Integration Inc. Target ranging using information from two objects
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US20110227783A1 (en) * 2008-01-31 2011-09-22 BAE Systems Information and Electronic Systems Inc Determining at least one coordinate of an object using intersecting surfaces
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Cited By (30)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4021802A (en) * 1975-07-29 1977-05-03 Litchstreet Co. Collision avoidance system
US4115771A (en) * 1976-05-11 1978-09-19 Litchstreet Co. Passive ATCRBS using signals of remote SSR
US4293857A (en) * 1979-08-10 1981-10-06 Baldwin Edwin L Collision avoidance warning system
US4486755A (en) * 1982-02-22 1984-12-04 Litchstreet Co. Collision avoidance system
US4642648A (en) * 1982-02-22 1987-02-10 Litchstreet Co. Simple passive/active proximity warning system
WO1985004259A1 (en) * 1984-03-14 1985-09-26 Litchstreet Co. Simple passive/active proximity warning system
US4768036A (en) * 1985-10-16 1988-08-30 Litchstreet Co. Collision avoidance system
US4894810A (en) * 1986-01-28 1990-01-16 Mikrovalmiste U.J. Pulkkanen Oy Method and a device for measuring a distance by means of ultrasonic pulses
DE3637129A1 (de) * 1986-10-31 1988-05-11 Deutsche Forsch Luft Raumfahrt Verfahren zur positionsbestimmung eines flugzeuges in einem dreiweg-dme-system
US4910526A (en) * 1987-05-18 1990-03-20 Avion Systems, Inc. Airborne surveillance method and system
US5075694A (en) * 1987-05-18 1991-12-24 Avion Systems, Inc. Airborne surveillance method and system
US4789865A (en) * 1987-10-21 1988-12-06 Litchstreet Co. Collision avoidance system
US5327145A (en) * 1990-05-22 1994-07-05 Hughes Aircraft Company Time delay passive ranging technique
US5552788A (en) * 1995-06-30 1996-09-03 Ryan International Corporation Antenna arrangement and aircraft collision avoidance system
US20030142002A1 (en) * 2000-05-09 2003-07-31 Karl Winner Vehicle surveillance system
US6816105B2 (en) * 2000-05-09 2004-11-09 Karl Winner Vehicle surveillance system
US20050024256A1 (en) * 2003-07-29 2005-02-03 Navaero Ab Passive Airborne Collision Warning Device and Method
US6985103B2 (en) 2003-07-29 2006-01-10 Navaero Ab Passive airborne collision warning device and method
US20050073439A1 (en) * 2003-10-01 2005-04-07 Perricone Nicholas V. Threat detection system interface
US7132928B2 (en) 2003-10-01 2006-11-07 Perricone Nicholas V Threat detection system interface
US20100156697A1 (en) * 2008-01-31 2010-06-24 Bae Systems Information And Electronic Systems Integration Inc. Quantity smoother
US20090231181A1 (en) * 2008-01-31 2009-09-17 Bae Systems Information And Electronic Systems Integration Inc. Target ranging using information from two objects
US20110227783A1 (en) * 2008-01-31 2011-09-22 BAE Systems Information and Electronic Systems Inc Determining at least one coordinate of an object using intersecting surfaces
US8081106B2 (en) * 2008-01-31 2011-12-20 Bae Systems Information And Electric Systems Integration Inc. Target ranging using information from two objects
US8164510B2 (en) 2008-01-31 2012-04-24 Bae Systems Information And Electronic Systems Integration Inc. Quantity smoother
US8436762B2 (en) 2008-01-31 2013-05-07 Bae Systems Information And Electronic Systems Integration Inc. Determining at least one coordinate of an object using intersecting surfaces
US9341705B2 (en) 2008-01-31 2016-05-17 Bae Systems Information And Electronic Systems Integration Inc. Passive ranging of a target
US20210124375A1 (en) * 2019-10-25 2021-04-29 Seamatica Aerospace Ltd. Method and apparatus for ensuring aviation safety in the presence of ownship aircrafts
CN111028550A (zh) * 2019-12-20 2020-04-17 成都纵横自动化技术股份有限公司 碰撞冲突检测方法及相关装置
CN111028550B (zh) * 2019-12-20 2021-07-13 成都纵横自动化技术股份有限公司 碰撞冲突检测方法及相关装置

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Publication number Publication date
FR2260116A1 (no) 1975-08-29
FR2260116B1 (no) 1980-09-12
GB1463388A (en) 1977-02-02

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